The present invention relates to a three-step process for removing water-soluble organics from produced water. In the first step, the organics-containing water is contacted with acid to reduce the solubility of the dissolved organics. In the second step, the acidified water is contacted and thoroughly mixed with a free oil to coalesce the dissolved organics. In the third step, the free oil phase is separated from the aqueous phase to produce substantially organic-free produced water.
A variety of industrial processes generate aqueous waste streams containing contaminating amounts of organic compounds. Before such streams can be discharged into a receiving body of water, the organics content must be substantially reduced to meet state and federal regulatory standards.
For example, offshore oil platform operations may generate production water waste streams. Some produced water contains naturally-occurring brines associated with and in contact with naturally-occurring petroleum in subsurface geologic formations and is produced as a consequence of producing the petroleum. The water may contain significant amounts of dissolved organic acids and other contaminating hydrocarbons. The main problem is that it contains carboxylic acid salts such as salts of naphthenic acids. If not removed, these contaminants are measured as oil and grease when the water is acidified and freonextracted, pursuant to EPA gravimetric test methods. Thus, it is desirable to treat such water so that it can be discharged without violating regulatory standards.
Produced waters that do not contain dissolved organic acids can be treated by settling (i.e., gravity separation) and flotation techniques. But we have found conventional oil/water separation techniques to be inadequate in removing water-soluble organics. For example, when water-soluble organics are present, high levels of oil and grease are measured even after gravity separation followed by induced air flotation.
Previous workers in the field attempted to remove dissolved organic contaminants by acidification. They believed that the dissolved organic acids would form a free oil phase at low pH's and could be removed by settling or flotation. For example, U.S. Pat. No. 4,401,570 discloses a method of removing organic esters from waste water using acidification. We have found, however, that these organics are too finely dispersed to allow them to settle or float. Thus, the organics remained and continued to result in unacceptable levels of oil and grease in the produced water stream.
Accordingly, it is the principle object of this invention to economically remove water-soluble organics from contaminated produced water streams.
In a preferred embodiment, the process of this invention comprises: acidifying the produced water, having 40-400 ppm dissolved organics, with sulfuric acid; contacting the acidified water with a free oil comprising a crude oil having an API gravity ranging from about 22.degree. to about 35.degree. to form a mixture; agitating the mixture to produce a thoroughly mixed phase; and separating the mixed phase to produce a free oil phase and a clean water phase.